Vantaggi
Even if you are "over-qualified" for some of their positions they will take you. In this day and age when people are looking for any job just to make something, that means a lot. Another plus is, for a staffing/temping agency, they have benefits. Other similar agencies or companies don't offer benefits.
Svantaggi
Pay can be very minimal. You are paid according to the requirements of the clients they support and not an across the board rate. I started at $18/hr for my first project. My next one was only $11/hr! Though the recruiters say contact them one month out when / before assignment is about to end, you really can't predict how long the client will actually need you. My first client said they will need us for 6 months when it was only 3 WEEKS they needed us!